In general, this invention relates to intervertebral spacers and their use in orthopedic treatment. More specifically, the present invention is directed to intervertebral spacers composed of a shape memory polymeric material. The intervertebral spacers can be deformed and induced to recover their original configuration as desired to facilitate orthopedic treatment of spinal defects.
Removal of damaged or diseased discs and implantation of intervertebral spacers into the disc space are known medical procedures used to restore disc space height, and to treat chronic back pain and other ailments. The spacers can be formed of a variety of materials—both resorbable and non-resorbable materials—including bone-derived material, metallic, ceramic, and polymeric materials. Typically, spacers are pre-formed into a general configuration that is easy to fabricate or, in selected examples, spacers are pre-formed to a generalized configuration that resembles idealized vertebral endplates. During surgery, the vertebral endplates must be prepared to receive the spacers. This typically involves either partial or full discectomy to remove the damaged or diseased disc. Thereafter the bone tissue of the vertebral endplates is cut in preparation to receive the spacer. It is also desirable to promote fusion between the vertebral bodies that are adjacent to the damaged or diseased discs. The endplates are often shaved, exposing the cancellous bone tissue in the vertebral body, to enhance the fusion between the vertebrae. Additionally, an osteogenic material is combined with a spacer—typically packed inside the spacer body and in the disc space around the space—to further promote bone growth.
Current surgical techniques approach the disc space from a variety of directions, including anteriorly, posteriorly, posterior-laterally and anterior-laterally. Regardless of the direction of approach, the surgery is extremely difficult, and several organs, vessels and nerve structures must be avoided. From the posterior approach, surgeons must be very careful to avoid the spinal cord and associated nerves. An oblique approach, such as from a posterior lateral or anterior lateral direction, offers many advantages. However, the oblique approaches only afford access to one side of the disc space. Obviously, it is desirable to avoid multiple incisions into the patient. Further smaller incisions and narrow passageways into the targeted disc space decrease the patients post surgical pain and recovery time. Further complicating the situation, the exposed cancellous bone tissue central to the vertebral body is spongy and an implanted spacer can subside into the tissue.
Therefore, it would be desirable to provide a spacer capable of withstanding the biomechanical loads exerted by the spinal column without subsiding into the spongy cancellous bone tissue. The spacer should also bear against strong cortical bone around the periphery of the endplates. Yet the space should be capable of being inserted into the disc space via a minimally invasive route.
Thus, in view of the above-described problems, there continues to be a need for advancement in the relevant field, including spacers for treatment of spinal defects and methods of treating spinal defects. The present invention is such an advancement and provides a wide variety of additional benefits and advantages.